Stretching fixture with quadrilateral linkage control of stretch head movements



Aug. 5, 1969 c. J. BATH 3,459,025

STRETCHING FIXTURE WITH QUADRILA'IERAL LINKAGE CONTROL OF STRETCH HEAD MOVEMENTS Filed Dec. 7, 1967 4 Sheets-Sheet 1 BY I M i "inrmemzx INVENTOR.

Aug. 5, 1969 c. J. BATH 3,459,025

STRETCHING FIXTURE WITH QUADRILATERAL LINKAGE CONTROL OF STRETCH HEAD MOVEMENTS Filed Dec. '7, 1967 4 Sheets-Sheet. 8

% BY a v l 6 A,

Aug. 5, 1969 J. TH

, STRETCHING FIXTURE WITH QUADRILATERAL LINKAGE CONTROL OF STRETCH HEAD MOVEMENTS T v INVENTOR, 5 573 Z Z. ,I

Arrow/5k Aug. 5, 1969v J TH 3,459,025

S'IRETCHING FIXTURE WI TH QUADRILATERAL LINKAGE CONTROL OF STRETCH HEAD MOVEMENTS Filed Dec. 7. 1967 4 Sheets-Sheet. 4

I INVENTOR. BY

3/1 rrae/vex United States Patent m US. Cl. 72-296 Claims ABSTRACT OF THE DISCLOSURE The stretching fixture of this invention is used in stretching sheet metal stock in one dimension by means of stretch heads which are caused to grip two opposite margins of a sheet of stock and then are moved in predetermined paths such that they stretch the sheet in said dimension and wrap it about the convex forming face of a male die. The path of each head is predetermined by a plurality of identical quadrilateral linkages which are shown as aligned with each other transversely of the tensioning dimension with their pivots at their corresponding apices coaxial. Each linkage has its pivotal axis at its inboard end in fixed position relative to the die and its pivotal axis at its outboard end in fixed position relative to the head. Each link is of fixed length.

The specific improvement is that, as to each quadrilateral linkage of the same head, at least one link is of a ditferent length than the link opposite it, whereby the associated head is caused to rock relative to its starting or loading position about axes parallel to said pivotal axes as it is moved along its predetermined path. The axes of each quadrilateral linkage, therefore, define either a trapezoid or a trapezium, as distinguished from a parallelogram.

This invention relates to a stretching fixture and combination thereof with a drawing die press, and is an improvement on the inventions disclosed in the U.S. patent of Robert A. Mackenzie, No. 3,314,269, issued Apr. 18, 1967, entitled Prestretch Fixture and Combination Thereof with Drawing Die Press, and in the application of Cyril J. Bath et al., Ser. No. 608,669, filed Jan. 11, 1967, and entitled Stretch Wrapping Fixture and Combination Thereof with Drawing Dies and Press.

In the above-entitled patent there in disclosed a conventional draw press employing complementary drawing dies combined with stock gripping stretch heads. The stretch heads are mounted on carriers which are movably connected to elevators and which support the heads for horizontal movement, relative to supporting elevators, toward and away from each other for tensioning the stock. The elevators, in turn, are mounted on a frame for vertical sliding movement and are power driven by hydraulic piston and cylinder assemblages or other means for lowering and raising the carriers, and thereby the heads. The heads are moved relative to the elevators, during lowering of the elevators, by rigid links so as to tension the stock to its yield point. The combined action of the links and elevators causes the heads to wrap the tensioned stock about the male die for stretch forming, or preparatory to stretch drawing the stock to final shape, as the case may be. The heads are maintained in substantial parallelism with their starting position at all times.

With the pivot points of the links located in proper position relative to the dies and to the heads of their carriages, the heads can be caused to follow precise preselected paths repeatedly such that the heads cooperate 3,459,025 Patented Aug. 5, 1969 properly and consistently with asymmetrical drawing dies and duplicate repeatedly the shape and overall dimensions of the formed, but untrimmed, sheet of stock.

The linkages connected the carriers to the elevators, and the elevators and carriers insured that the heads would remain substantially parallel to their starting or loading positions. This assured that the heads could approach very closely the ends of the dies, thus reducing the length of the sheet required for a given part or group of parts.

Application Ser. No. 608,669, discloses a structure from which the elevators are eliminated and, instead, the stretch heads are both supported and guided along precise paths and maintained in parallelism with their loading positions during the stretch drawing operation by means of head supporting parallelogram linkages of which the pivotal axes at one end of the linkages of each head are in fixed relation to the male die and at the other are in fixed relation to the associated head. The intersections of the pivotal axes of the pairs of links of a given parallelogram linkage with a plane normal to these axes, define a parallelogram. Such a parallelogram linkage supports the associated head and maintains it parallel to its original starting or loading position during operation and constrains the head to follow precisely its proper predetermined path invariably.

This structure is particularly useful for high speed production of automobile body parts in that, among other things, it permits the gripping jaws to approach substantially to the end limits of the die in the tensioning dimension so that very little metal is wasted in trim.

However, in connection with airplane parts, quite often a substantial amount of metal extends beyond the end limits of the die. Also, the metals used for airplanes and rockets do not lend themselves to abrupt bends. In such cases the margin of the sheet of metal gripped between the stretch head jaws and the contiguous portion of the sheet of metal between the end of the die should be a continuous surface free from abrupt folds and bends.

Generally, this requires that the gripped margin extend tangentially relative to the end of the forming surface of the die at the end of the forming operation.

It has been found that this effect can be obtained by use of non-parallelogram quadrilateral linkages, as to each of which the axes define a quadrilateral at least one side of which is of a length different from the length of the side opposite to it. Thus the quadrilateral is either a trapezium or a trapezoid. Such linkages not only cause the heads to follow the general path desired for the particular forming operation as in the above application, but they also can be selected to impose on the head controlled rocking movements about axes parallel to the linkage axes to various tilted positions, relative to the starting position, in which the stock between the end of the die and also that portion of the stock gripped by the jaws of the stretch head will form a continuous surface tangent to the forming die surface at the instantaeous point of tangency of the stock already in contact with the forming surface of the die. Also, in some cases, it is desirable to bow the sheet upwardly when loading it into the jaws, so that it assumes the shape of an arch and becomes selfsupporting against downward sagging. The links can be chosen so that the position of the heads for loading is one in which the jaw throats slope upwardly inwardly endwise of the die toward their upper ends, and can readily be loaded with the sheet in arched condition. Also, when desired, the heads can be thus rocked to maintain the tangency at preselected portions of their paths of travel and selected non-tangent relations at other portions of their path.

Specific objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a front elevation of a stretch head and die combination which may be used for stretch forming or stretch drawing between companion male and female drawing dies in a stretch press, and embodying the quadrilateral linkage of the present invention for controlling the paths of the stretch heads, respectively;

FIG. 2 is a top plan view of the structure illustrated in FIG. 1;

FIG. 3 is a diagrammatic illustration on a reduced scale showing the location and rocked position of the lefthand stretch head in FIG. 1 at the beginning and end of the forming operation;

FIG. 4 is a side elevation of a structure similar to FIG. 1 showing a modified quadrilateral linkage for controlling the path and tilted position of the stretch head;

FIG. 5 is a diagrammatic illustration on a reduced scale showing the location and rocked position of the lefthand head in FIG. 4 at the beginning and end of the drawing operations; and

FIG. 6 is a diagrammatic illustration showing two stretching fixtures installed in a drawing die press for stretch drawing.

Referring to the drawings, the structure is shown as mounted on a horizontal bolster 1 of which at least the longitudinal central portion is adapted to rest on the bed of a conventional power driven draw die press. Supported on the bolster 1, through the medium of a plurality of rigid spacer blocks 2, is a drawing die 3. In the form illustrated, the die is a male die having an upwardly convex forming face. The die is assumed to be one for forming airplane parts in which a considerable amount of the metal stock S in the finished shape will extend considerably beyond the ends of the forming face of the die 3, the amount depending upon the particular part being formed.

In order to stretch the stock about the die 3, either for stretch forming or preparation to stretch-drawing it between companion drawing dies, suitable stretch heads 4 are provided, and are spaced from the ends of the die, one at each end of the die in the drawing direction. Each head comprises a stationary jaw 5 and a movable jaw 6 connected together by a pivot 7 for rocking into stock gripping and releasing positions. The jaws are operated by suitable linkages 8 driven by a piston and cylinder assemblage 4 which may be of the air or hydraulic fluid type. The head 9 is supported on a carrier 10 having brackets 11 at its ends to which are pivotally connected, by pivots 12, pistons rods 13 of reversible piston and cylinder assemblages 14 which preferably are of the hydraulic type controlled by a conventional reversing valve.

In order to constrain the head to move along a preselected path and to rock about axes extending forwardly and rearwardly of the heads and bolster block .1, the quadrilateral linkage means of the present invention are provided.

In the form illustrated, the linkage means for the heads comprise linkages at the front and rear of the beads, respectively, as illustrated in FIG. 2. Each linkage of the left-hand head in FIG. 1 includes an upper side link 15 and a lower side link 16. Each of the links 15 and 16 is fixed in length and each is pivoted at one end so as to rock about an axis which is in fixed position relative to the head 4 and at the other end so as to rock about an axis which is fixed in position relative to the die 3. For example, a pivot 17 at the outboard end of the link 15 is in fixed position relative to the head 4 and a pivot :18 at the inboard end of the link 15 is in fixed position relative to the die. Correspondingly, a pivot 19 at the out board end of the link 16 is in fixed position relative to the head and the pivot 20 at the inboard end of the link 16 is in fixed position relative to the die. The end links are provided, respectively, by the portion of the carrier 10 to which the pivots 17 and 19 are connected, and by the portion of a fixed supported 21 to which the pivots 18 and 20 are connected. The supports 20 are secured in fixed position relative to the die 3. The axes of all of these pivots are parallel to each other and define in a plane normal to the axes a quadrilateral which is either a trapezium, as illustrated in FIG. 1, or a trapezoid, as illustrated in FIG. 4.

Starting with the head 4 in a loading position, the throat of the jaws 5 and 6 are horizontal and extend forwardly and rearwardly of the bolster 1 or press in which the bolster is supported. Thus the throat is at a height to receive the sheet edgewise for supporting it out of contact with the face of the die 3. As the heads are swung downwardly by operation of the assemblages 14, they are constrained by the links 15 and 16 to move outwardly, or in some cases outwardly and then back inwardly, as the heads move downwardly. By this action the stock is wrapped about the die 3 while tensioned into its yield range. At the same time, since the axes of the linkages do not form parallelograms, the head 4 is caused to rock about axes parallel to the axes of the links. Generally the lengths of the links 15 and 16 are chosen so that the left-hand head in FIG. 1 rocks counterclockwise to a degree such that at the end of the stretching operation the jaws slope upwardly toward the die so that the gripped edge of the stock, indicated at 22, and the portion of the stock between the gripped margin 22 and the end of the die forming face indicated at 23, are lineal and are both tangent to the forming face of the die at 23. While, as illustrated in FIG. 3, the head 4 is shown as horizontal above the die in loading position, in some cases for loading it might be tilted slightly upwardly to the right so that the stock is arched and convex upwardly during loading as such arching prevents sagging of the stock and causes the stock to retain its initial loading position more effectively.

At the end of the forming operation the head is tilted so as to be tangent to the male die 3.

However, it may be that a female die is to be used which will force the metal downwardly further around the end of the die 3, in which case the final position of the head in FIG. 3 might be a tilted position in which the stock gripped by the head and the portion of the stock between the head and die would be tangent to the end of the forming surface of the female die. Again, different degrees of tilt of the head at dilferent positions of the head along its path of travel can be obtained, as desired.

The right-hand stretch head and its accompanying links are the same in general as the left-hand head and its links, except, of course, since the pieces to be formed may be asymmetrical, the axes of the links at the right-hand will form a different quadrilateral pattern than the axes of the links at the left-hand end.

In FIG. 4 there is illustrated a modification of the structure illustrated in FIG. 1, in which the quadrilateral linkages of the head 4a each comprises upper and lower links 15a and 16a. These links are arranged so that their pivoted axes at their outboard ends are secured to the heads in fixed position relative to each other and the axes at their inboard ends are secured to a suitable support 23a arranged in fixed position at the outboard end of the forming die 3a. These axes define a trapezoid, as distinguished from a trapezium, but not a parallelogram.

The press and its operation, and control of the stretch units, may in all other respects be such as described in the above-identified patent, or, as mentioned, the stretching and die assemblage may be used separately for stretch forming, as distinguished from stretch drawing between companion dies.

For stretch drawing, one or two of the stretching fixtures may be mounted in a drawing press 25 having a ram 26 which may be driven in any conventional manner; for example, by reversible hydraulic piston and cylinder assemblages 27. Hydraulic fluid is supplied to the assemblages 27 through a control valve 28 from a pump 29 driven by a motor 30.

The assemblages 14 of the fixtures are driven independently of each other by hydraulic fluid supplied by a pump 31 driven by a motor 32. The assemblages for each head are connected in parallel with the pump through their common control valve 33.

Conventional air or hydraulic pressure may be used to open and close the jaws.

Generally two stretch heads are employed and are located one at each end of the die, as illustrated. In some cases, however, one of the heads may be stationary and in fixed position relative to the die.

Having thus described my invention, I claim:

1. A stretch wrapping unit comprising:

a stretch head arranged to grip a margin of a sheet of stock for applying tensioning force along one dimension thereof stretching the stock and wrapping the stock over a male die while holding the stock under tension when the head is moved along a predetermined fixed invariable path;

power means for moving the head;

quadrilateral linkage means for the head for constraining the head to follow said path during movement of the head by the power means;

means connecting the outboard end of the linkage means to the head with the pivotal axes of the linkage means at said outboard end parallel and in fixed position relative to the head;

supporting means connected to the inboard end of the linkage means and supporting said inboard end with the pivotal axes at said other end in fixed position relative to each other and to said path;

characterized in that the pivotal axes at the apices of the linkage means define, on a plane normal to the pivotal axes, a quadrilateral of which at least two of the opposite sides diifer in length from each other.

2. The structure according to claim 1 wherein each linkage means comprises a plurality of quadrilateral linkages, and the quadrilaterals defined by the four pivotal axes at the apices of the respective linkages, are substantial duplicates of each other.

3. The structure according to claim 2 wherein the linkages are positioned so that corresponding apices have common pivotal axes, respectively.

4. The structure according to claim 1 wherein a male die having a convex forming face is provided, and the supporting means are in fixed position relative to one end of the die and maintain said inboard end of the linkage means with the pivotal axes at said inboard end in fixed position relative to the die.

5. The structure according to claim 4 wherein the die has a first portion body integral with a portion having the forming face, said first body portion is the supporting means, and the pivotal connections of the linkage means with the first body portion are spaced from the surface of the face and extend generally transversely relative to said surface and die.

6. The structure according to claim 1 wherein power means are provided for moving the head along said path.

7. The structure according to claim 1 wherein the linkage means comprise a plurality of quadrilateral linkages, two opposite sides of each linkage are compression resisting links each link of which is pivotally connected at its outboard end of the head and at its inboard end to the supporting means.

8. The structure according to claim 7 wherein the axes of each quadrilateral linkage for an associated head defines a trapezoid.

9. The structure according to claim 7 wherein the axes of each quadrilateral linkage for an associated head defines a trapezium.

10. The structure according to claim 4 wherein a second stretch head is arranged at the opposite end of the die and is operable independently of the first mentioned head to grip the opposite margin of the stock.

References Cited UNITED STATES PATENTS 2,442,268 5/1948 Fields et a1. 72297 3,302,437 2/ 1967 Dolney 72--302 3,314,269 4/ 1967 Mackenzie 72450 RONALD D. GREFE, Primary Examiner US. Cl. X.R. 

